Oval grinding



A. L. NELSON OVAL GRINDING Aug. 11, 1931.

Filed Ma 5. 1928 2 Sheets-Sheet l 1931- A. L. NELSON 1,818,085

OVAL GRINDING Filed May 5, 1928 2 Sheets-Sheet 2 Patented Aug. 11, 1931 UNITED STATES PATENT OFFICE ADOLPE n NELSON, or

DETROIT, MICHIGAN, ASSIGNOR TO IBOHN ALUMINUM & BRASS CORPORATION, OF DETROIT, MICHIGAN OVAL GRINDING Application filed May 5, 192a. Serial No. 275,317.

This invention relates to a method of grinding hollow articles, such as pistons. i

A particular object is the provision of a simple and effective method of grinding a I hollow article in such a manner as to give the finished product an oval exterior shape. The process is particularly applicable to the grinding of pistons for internal combustion engines where the open end of the piston is to be given an oval shape.

While preferred methods of carrying out the process have been disclosed herein, it will be clear that the process may be modified without departing from the spirit and scope 1a of the invention as hereinafter set forth and claimed.

In the drawings;

Fig.1 is an elevation of apparatus adapted to the process of the invention.

Fig. 2 is a section on line 22 of Fig. 1.

Fig. 3 is a bottom plan of a piston treated according to the invention.

Fig. 4 is a view similar to Fig. 3 but illus-' trating a modified process.

Fi 5 is a section similar to Fig. 2 but showmg the method of grinding the piston of Fig. 4:. i I

Fig. 6 is a view similar to Fig. 4 showing the result of the grinding operation.

In finish grinding the exterior surface of certain hollow cylindrical objects it is sometimes desired to grind them to a slightly oval shape. For example certain considerations of operating efficiency may make it desirable to grind the skirt of an automobile piston in suc a manner as to produce a slight oval on the exterior of the slnrt adjacent its open end. According to current practice this result can be obtained-only by cam grinding, a process which involvesdifliculties and high cost.

The 'rocess of the present invention is adap for finishing articles of resilient material and consists broadly in first expanding the open end of'the hollow cylindrical member into an oval shape, and then grindingthe member in the usual manner until the exterior surface of the expanded.-:

' cylinder is, P rfe ly cylindrical. After grinding, the-finding means is released, 59 and due to the erent resiliency of the cyl-' inder walls they spring back to their original position, and the parts that I Were expanded out beyond the normal circumference of thecylinder and lost more material in the grinding operation, now lie slightly below .1 the normal circumference, giving the cylinder an oval exterior shape.

.The drawings illustrate particularly how the invention may be applied in grinding a piston for an internal combustion engine. 00 The reference numeral 10 indicates the table of a grinding machine, the driving center 11 being supported in a journal bracket 12 and rotated by any suitable means. The drivin center 11 ismade slightly oval, the amount 0 deviation from the normal circle being made to suit the particular circumstances, in one instance being about 0.003 in. A centering member 13 is mounted in the upper end of the bracket 14, the member 13 being springpressed toward the driving center 11. A driving pin 15 projects from driving center 11 for the purpose of engaging the work and causing it to maintain its original position on the driving center. y

The piston comprises a head 16 and a skirt 17, and is formed with bosses 18 for thepiston pin on opposite sides. In the particular example itis desired to grind thelower end of the skirt so that the part of its surface lying under the pin bosses will be reduced below the normal circumferenceof the skirt. This is done by placing the open end of the piston on the drlvmg center 11 with the major axis of the driving center coinciding with the diameter A -A of the piston, which is parallel with the axis of the pin bosses. The piston is then sprung over the driving center 11 so that its lower end changes shape from the normal round circumference indicated in dotted lines in Fig. 2 to the oval shape shown in solid lines in- Fig. 2. The tapered resilient holding center 13 is then engaged in a hole 19 formed in the head of the pistoii, the pressure of center 13 being suflicient to maintain the piston in its expanded position. The driving pin 15 engages a part of the piston and keeps the piston from slipping ,on the drivin center.

e grinding of the skirt is now proceeded with by means of the usual grinding tools until the exterior of the expanded piston has acquired a true cylindrical contour.

When the grinding is completed the piston is removed from the machine, and the resilv normal round circumference indicated in dotted lines.

Figs. 4, 5 and 6 of the drawings illustrate another method of grinding by means of which a similar result is obtained.

In this case the conical centering hole 22 in the open end of the piston skirt, which must be machined in the open end of the piston skirt to aiford a seat for the center 11, is formed while the lower end of the skirt is held in slightly flattened condition. In this manner the centering hole is given an oval shape and isarranged so that its short axis coincides with the axis AA of the piston, which is parallel with the axis of the pin bosses.

The driving center 20 used in this applica tion of the invention is similar to the center 11 of Fig. 1, but instead of being oval is round. hen the center 20 is pressed into the oval centering hole, the general arrangement being similar to that of Fig. 1, the spring tension forcing the center 20 into the piston is sufiicient to press the walls of the skirt on axis AA outwardly until the entire inner periphery of the centering hole is in contact with the center 20. In this position, which is shown in Fig. 5, the outer periphery ofthe skirt is pressed outwardly on axis A-A from its original circular shape indicated in dotted lines at 21 in Fig. 5 to the full line position.

The piston is now ground with the usual grinding implements, and the grinding is continued until the outer surface of the skirt has been reduced to a true cylinder, which means that more material must be taken off at the parts lying on axis A-A than on the axis at right angles thereto.

After the finish grinding the piston is removed from the centers, and the inner periphery of the wall 19 then'returns to its oramaoee 7 It will be evident from this disclosure that the amount of ovalness in the resulting piston is greatest at the-lower end of the piston and progressively becomes less toward the top of the skirt.

A person skilled in the art will erce1vlindrical article having a closed end whichcomprises holding a true center on the closed end, expanding the open end into oval exterior shape, grinding the exterior surface of the expanded cylinder into truly cylindrical shape, and then releasing the expanded end to permit the exterior circumference thereof to assume an oval shape.

3. The method of finishing a piston having a closed head and pin bosses which comprises expanding the open end into oval exterior shape with the major axis parallel to the axis of the pin bosses, grinding the exterior surface of the expanded piston into truly cylindrical shape, and then releasing the expanded end to permit the exterior circumference thereof to assume an oval shape.

4- The method of finishing a piston having a closed head and pin bosses which comprises holding a true center on the closed head, expanding the open end into oval exterior sha with the major axis parallel. to the axis of tii: pin bosses, grinding the exterior surface of the expanded piston into truly cylindrical shape, and then releasing the expanded end to permit the. exterior circumference thereof to assume an oval shape.

In testimony whereof I afiix my signature.

' ADOLPI-I L. NELSON.

iginal shape, due to the resiliency of the skirt material. This means that the parts of the outer periphery lying on'axis A-A fall below the true cylindrical shape indicated on dotted lines in Fig 6. thereby reducing the outside diameter of the skirt on axis AA below the piston pin bosses tothe full line position of Fig i.

The eccentricities and changes of shape have been shown on an exaggerated scale in the drawings to make the subject matter clear. 

